I was looking into getting a German plate for my car as well. I JUST ran into this:
Looks like a universal frame that should work.
If not, check this out:
near the bottom of the page, you'll see that they have a "German Bolt Kit (BOLT-GERM) $5.00 - German fastener kit. Made especially for our authentic Euro-Plates".
[Edited by wjm on 04-23-2001 at 01:05 PM]